−Cl and
−CH3 groups are
o and
p directing. They are electron releasing due to
+M and hyperconjugation effects. Further since such groups increase electron density in the nucleus, they facilitate further electrophilic substitutionand hence known as activating group. The activating effect of these groups is in order of
−CH3>−X but chlorine exceptionally deactive the ring due to strong
− I effect. Hence, it is difficult to carry out substitution in chlorobenzene thanin benzene. Further
−NO2 is a deactivating group, hence deactivates the benzene nucleus, i.e. hinder the further substitution. Thus nitrobenzene undergo electrophilic substitution with a great difficulty, hence the correct order will be